Nitinol Spring Through Tubing Bridge Plug

ABSTRACT

A bridge plug assembly that can be set in a wellbore tubular using wellbore pressure to form a pressure differential on a piston that actuates sliding members. A resilient member, such as a spring, is compressed from a downhole pressure differential. The bridge plug assembly can be removed by equalizing pressure across the piston and the spring. The spring can expand and re-stow the expanded plug. The plug can be formed from a nickel titanium alloy flexible member that can be selectively radially expanded so its outer surface sealingly engages a surrounding tubular. The percentage of weight of nickel can range up to about 40 to about 58%, 55% or to about 60%.

RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalApplication No. 61/166,489, filed on Apr. 3, 2009, the full disclosureof which is hereby incorporated by reference herein.

BACKGROUND

1. Field of Invention

The invention relates generally to the field of oil and gas production.More specifically, the present invention relates to a system and methodfor plugging tubing within a borehole.

2. Description of Prior Art

Downhole plugs are used to block flow through a wellbore tubular and canbe formed from an elastomeric membrane on a mandrel or coaxially stackedmembers. Downhole plugs can be selectively set into place by expandingthe membrane or collapsing the stacked members to block the annularspace within the mandrel. Plug or packer setting can occur by axiallycompressing the mandrel or by filling the membrane with a pressurizedfluid. The tubulars can be casing or production tubing.

SUMMARY OF INVENTION

Disclosed herein is a bridge plug that can be set to block flow in atubular, or to block flow in an annulus between two tubulars. In oneexample, the plug includes a nickel titanium alloy flexible member thatcan be selectively radially expanded so its outer surface sealinglyengages a surrounding tubular. In an example embodiment a bridge plugassembly for plugging a tubular within a wellbore is described hereinthat includes an elongate mandrel, an actuation sleeve circumscribingthe mandrel, a first reservoir within the actuation sleeve, a plugsection on the mandrel and adjacent the actuation sleeve and selectivelymoveable from a substantially cylindrical insertion configuration to aradially bulging plugging configuration, a second reservoir disposedbetween the first reservoir and the plug section, and a sealing barrierbetween the first and second reservoir and coupled to the actuationsleeve. When pressure in the first reservoir is greater than the secondreservoir pressure it pushes the barrier into the second reservoir, thisin turn urges the actuation sleeve into compressive engagement with theplug section and convert the plug section to the radially bulgingplugging configuration. Valves that selectively open and close may beincluded that each have an end in fluid communication with the wellboreand an opposite end in fluid communication with the first reservoir,other valves may have an end in fluid communication with the wellboreand an opposite end in fluid communication with the second reservoir. Aflow circuit can be in the mandrel that is made up of interconnectedaxial and radial passages, a valve actuator can be included that iscoupled with the mandrel and selectively provides fluid communicationbetween the flow circuit and the second reservoir. Another flow circuitmay be set in the mandrel that is made up of axial and radial passagesthat interconnect, a valve actuator can be coupled with the mandrel thatselectively provides fluid communication between the first reservoir andthe second reservoir. A deployment module can be included that isattachable to an end of the actuation sleeve. The bridge plug assemblymay further include a spring coaxially disposed in the mandrel andselectively compressible. Equalizing fluid pressure across the barrierallows the spring to axially expand and selectively move the plugsection back to the substantially cylindrical insertion configurationfrom the radially protruding configuration. An outer shell made of anickel titanium alloy can be optionally included on the outer peripheryof the plug section.

Also included and described herein is a method of plugging a tubularwithin a wellbore. In an example the method includes providing a bridgeplug assembly in the tubular. The bridge plug assembly can have amandrel, an actuation sleeve circumscribing the mandrel. Adjacent thesleeve can be a plug element on the mandrel that is selectivelyconfigurable between a substantially cylindrical configuration to abulbous configuration. By axially urging the actuation sleeve againstthe plug element the plug element changes from the substantiallycylindrical configuration into the bulbous configuration to plug thetubular. Urging the sleeve can be done by directing pressure from thewellbore along the axis of the bridge plug assembly. The bridge plugassembly can further include a reservoir and a piston that is axiallyslidable into the reservoir; the piston can be coupled with theactuation sleeve. A resilient member can be axially disposed in themandrel, an example embodiment of a step of the method includescompressing the spring by forming a pressure differential along thespring. Removing the pressure differential along the spring enables thespring to exert an expansive force. Directing the spring force acrossthe plug element can return the plug element to the substantiallycylindrical configuration from the bulbous configuration. In an exampleembodiment, the plug element is made of an outer shell formed from anickel titanium alloy, optionally, the plug element is made from anouter shell formed from an elastomer. A flow circuit may optionally beprovided in the mandrel formed from axial and radial passages thatinterconnect. Also included may be a valve actuator that is coupled withthe mandrel for selectively providing fluid communication between thefirst reservoir and the second reservoir. In an example step, the methoddescribed herein includes actuating the valve actuator to provide fluidcommunication between the first and second reservoirs. Another flowcircuit may be included in the mandrel also made up of interconnectedaxial and radial passages. A valve actuator can optionally be includedthat is coupled with the mandrel for selectively provides fluidcommunication between the flow circuit and the second reservoir. In anexample, the valve actuator is actuated to provide fluid communicationbetween the flow circuit and the second reservoir. An actuation modulecan be included with the bridge plug assembly and a step of removing theactuation module from the bridge plug assembly can be performed with theactuation module. The actuation module can be reattached to the bridgeplug assembly and a valve in the bridge plug assembly actuated toequalize pressure to the actuation sleeve. This moves the plug elementso that the plug element changes to the substantially cylindricalconfiguration from the bulbous configuration. The bridge plug assemblycan then be removed from the tubular. In an alternative example, theplug element is changed to the substantially cylindrical configurationfrom the bulbous configuration by compressing a spring within themandrel with a pressure differential, then removing the pressuredifferential along the spring. This releases the spring to exert anexpansion force, by directing the expansive force from the spring alongan axis of the plug element the plug element is returned to thesubstantially cylindrical configuration.

BRIEF DESCRIPTION OF DRAWINGS

Some of the features and benefits of the present invention having beenstated, others will become apparent as the description proceeds whentaken in conjunction with the accompanying drawings, in which:

FIGS. 1A-1C are side views an example of a through tubing bridge plugbeing set in a wellbore in accordance with embodiments of the presentdisclosure.

FIGS. 2A-2D are schematic views of an alternative through tubing bridgeplug.

FIGS. 3A-3D are side and sectional views of a plug for use in a bridgeplug assembly in an insertion configuration and expanded pluggingconfiguration.

FIGS. 4A-4C are sectional views an example of a through tubing bridgeplug being set in a wellbore in accordance with embodiments of thepresent disclosure.

While the invention will be described in connection with the preferredembodiments, it will be understood that it is not intended to limit theinvention to that embodiment. On the contrary, it is intended to coverall alternatives, modifications, and equivalents, as may be includedwithin the spirit and scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF INVENTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theillustrated embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Like numbers refer to like elements throughout. For the convenience inreferring to the accompanying figures, directional terms are used forreference and illustration only. For example, the directional terms suchas “upper”, “lower”, “above”, “below”, and the like are being used toillustrate a relational location.

It is to be understood that the invention is not limited to the exactdetails of construction, operation, exact materials, or embodimentsshown and described, as modifications and equivalents will be apparentto one skilled in the art. In the drawings and specification, there havebeen disclosed illustrative embodiments of the invention and, althoughspecific terms are employed, they are used in a generic and descriptivesense only and not for the purpose of limitation. Accordingly, theinvention is therefore to be limited only by the scope of the appendedclaims.

The present disclosure is directed to a system that blocks or plugs theinside of a tubular, such as tubing, wherein the tubular is in awellbore. FIGS. 1A-1C illustrate in side view an example of a bridgeplug assembly 10 being set within a wellbore tubular. FIG. 1Aillustrates the bridge plug assembly 10 in an insertion or deployingmode, i.e., when being inserted from surface into the tubular. In thisembodiment, the bridge plug assembly 10 includes a series of elongatesections or modules coaxially coupled to one another. An annulardeployment module 12 is shown circumscribing a deployment mandrel 13that protrudes from within the deployment module 12 to define an end ofthe bridge plug assembly 10. An annular plunger module 16 telescopinglycircumscribes the deployment module 12 on an end distal the deploymentmandrel 13. The end of the plunger module 16 opposite the deploymentmodule 12 connects to an annular actuation module 24. A plug section 30couples on the end of the actuation module 24 distal from the plungermodule 16. A cylindrically shaped base sub 38 is shown attached on anend of the plug section 30. An inner mandrel 42 extends outward from theshaped base sub 38 in a direction opposite the plug section 30.

Illustrated in FIG. 1B is a side view example of the bridge plugassembly 10 being set within a tubular 8. As shown, the plug section 30is axially compressed causing its mid portion to expand radially outwardinto sealing contact with the tubular 8 inner circumference. The plungermodule 16 is shown in FIG. 1B having telescoped away from the deploymentmandrel 13 thereby exposing more surface area of the deployment module12. In one example embodiment, the inner mandrel 42 couples with thedeployment mandrel 13, and the base sub 38 anchors onto the innermandrel 42. Axially motivating the plunger module 16 against the plugsection 30 produces the outward radial deformation of the plug section30. In FIG. 1C, the bridge plug assembly 10 is shown in a fully set modewith the deployment module 12 having been removed from the rest of theassembly 10. When in the set mode, the bridge plug assembly 10 canremain within a tubular indefinitely.

FIGS. 2A-2D provide schematic views of an example of a bridge plugassembly 10A being used within a wellbore W. In this example fluidreservoirs R₁ and R₂ are provided within the plunger module 16A andactuation module 24A that are separated by a barrier B. The barrier Bmay be coupled with one of the plunger module 16A or actuation module24A Fluid is shown in the reservoirs R₁ and R₂, in an example the fluidis at a pressure less than the pressure ambient in the wellbore W. Aresilient member, such as a spring S is shown coaxially set within thebridge plug assembly 10A. Within the wellbore W, a valve V₁ can beactuated that ports higher pressure fluid from the wellbore W to thereservoir R₁, the barrier B seals between the reservoirs R₁ and R₂ sothat a force is applied to the barrier B and transferred to the plungermodule 16A and/or actuation module 24A. The plunger and actuationmodules 16A, 24A may telescope along the length of the plunger assembly10A, thus the axially applied force from the barrier B slides theplunger and actuation modules 16A, 24A towards the plug section 30A. Theplug section 30A, which includes a resilient outer shell 41, does nottelescope along the bridge plug assembly 10A, but is compressed causingthe resilient outer shell 41 to protrude radially outward as shown inFIG. 2B into contact with the tubular 8. Ports (not shown) may directfluid from reservoir R₂ to within the protruding outer shell 41.

Referring to FIG. 2C, the deployment module 12A, which in an exampleembodiment operates as a setting tool to actuate the bridge plugassembly 10A, has been removed thus allowing the bridge plug assembly10A to remain in the wellbore W and plug the tubular 8. By removing thedeployment module 12A, fluid pressure from the wellbore W communicatesto the spring S to form a compressed spring S_(C). Valves and/or portsconnected to the reservoirs R₁ and R₂ remain closed to seal the fluid inthe reservoirs R₁ and R₂. In FIG. 2D, deployment module 12A is beingreset into the bridge plug assembly 10A for retrieval of the bridge plugassembly 10A from within the wellbore W. Through the deployment module12A, or an alternative remote telemetry system, valve V₂ is opened sothat wellbore pressure can communicate into the plug section 30A andreservoir R₂ to equalize pressure between the barrier B. Without thepressure differential across the barrier B, the spring S can expand,when expanding the spring S exerts an axial force to the inner mandrel42A that is transferred to the base sub 38A. The deployment module 12Acouples into the plunger module 16A, so that the expanding springaxially stretches the plug section 30A to draw the outer shell 41radially inward as shown in FIG. 2D.

In an example, material for forming the outer shell 41 may include anickel titanium alloy, wherein the percentage of weight of nickel rangesup to about 60%, in one embodiment where it ranges from about 40 toabout 58% and in another embodiment about 55%. This alloy can be eitheran austenite or martensite phase. In an unstressed environment, thenickel titanium alloy can be in an austenite structure. It should benoted that in the configuration of FIGS. 2B and 2C, the outer shell 41has a planar section proximate to its midsection. Retaining the expandedmidsection as a planar configuration, enhances the sealing contactbetween the plug section 30A and tubular 8. Optionally, the outer shell41 can be made from an elastomeric material, a memory metal, orcombinations thereof.

FIGS. 3C and 3D illustrate examples of the plug section 30 in aninitially produced and expanded configuration that is used for sealingwithin the tubular 8 and are shown respectively in side perspectiveviews and a side partial sectional view. Referring now to FIG. 3C, theplug section 30 is shown having an outer flexible member 31 that encasesa helically-wound spring 32. The spring 32 is made up of a wound elasticspring member 36 encased in a laminate 37. Material for forming thespring member 36 may include a nickel titanium alloy, wherein thepercentage of weight of nickel ranges up to about 60%, in one embodimentwhere it ranges from about 40 to about 58% and in another embodimentabout 55%. This alloy can be either an austenite or martensite phase.The laminate 37 can be any elastic material including elastomers andpolymeric compounds. In this initial configuration the nickel titaniumalloy can be in an austenite structure. It should be noted that in theconfiguration of FIGS. 3C and 3D, the plug section 30 includes a planarsection proximate to its midsection. Retaining the expanded midsectionas a planar configuration, enhances the sealing contact between the plugsection 30 and tubular.

In an alternative example, the plug section 30 can be changed from thebulbous configuration of FIGS. 3C and 3D for insertion into a tubular 8by axially applying a torque about the axis A_(X) of the spring 32; asillustrated by the arrow in FIG. 3C. Converting the plug section 30 fortubular insertion forms the substantially cylindrical configurationdepicted in FIGS. 3A and 3B; where the insertion mode configuration ofthe plug section 30 is illustrated respectively in a side perspectiveview and a side partial sectional view. Fixing opposing ends of thespring 32 can retain the plug section 30 in the insertion configuration.The axial torque can be applied to the spring 32 before or after it iscoupled with the plug assembly 10. In the insertion configuration thenickel titanium alloy has an austenite-martensite structure. In anexample embodiment, the maximum deformation of the nickel titanium doesnot exceed 8%, optionally, the maximum deformation does not exceed 6%.By releasing one end of the spring 32, while in the insertionconfiguration, allows the spring 32 to unwind and return to the sealingconfiguration of FIGS. 2A and 2B.

FIGS. 4A-4C illustrate an example embodiment of the bridge plug assembly10 in a sectional view and depict sequences of setting the assembly 10within the tubular 8. Referring now to FIG. 4A, a sectional view of thedeployment module 12 is shown having inserted therein the deploymentmandrel 13. A deployment manifold 14 is formed through the mandrel 13. Ahousing 15 circumscribes the mandrel 13 to define an annular spacebetween the mandrel 13 and housing 15. The plunger module 16 includes anelongated plunger body 18 having a manifold 19 formed within the body18. The plunger module 16 includes an annular sleeve 17 disposed alongits outer periphery that is set radially outward from the body 18 todefine an annular plunger reservoir 20 between the body 18 and sleeve17. The plunger body 18 includes a mandrel-type portion having an outerattachment that lines the mandrel portion and radially transitionsoutward to provide a flange along the mandrel mid portion. The innerradius of the sleeve 17 is profiled to form an inwardly dependingshoulder 21 on an end of the sleeve proximate the actuation module 24.The reservoir 20 is disposed axially between the shoulder 21 and theflange on the plunger body 18.

A spring body 22 between the plunger module 16 and actuation module 24attaches coaxially with the plunger body 18. The spring body 22 includesa cylindrical cavity coaxially aligned with an axis A_(X) of theassembly 10; a spring 23 is shown disposed within the cavity. A passage29 provides fluid communication between the cavity and the spring body22 lower end. Included within the actuation module 24 is an actuationmandrel 27 shown substantially coaxial with the bridge plug assembly 10and having its upper end coupled to the spring body 22 lower end. Theactuation mandrel 27 includes a manifold 28 made up of an elongatedaxial passage formed through the mandrel 27 and passages lateral to theaxial passage. The axial passage of the manifold 28 is in fluidcommunication with the passage 29 on its upper end. Circumscribing theactuation mandrel 24 is an actuation sleeve 25 that couples with theplunger sleeve 17 on its upper end and extends into coupling arrangementwith the plug section 30 on its lower end. The actuation mandrel 27extends downward into the plug section 30 transitioning into a plugmandrel 33 within the plug section 30. The plug mandrel 33 extendsthrough the plug section 30 and transitions into the inner mandrel 42. Aplug manifold 34 extends through the plug and inner mandrels 33, 42 andincludes a lateral passage connecting with the space surrounding theplug mandrel 33 upper end. The base sub 38 includes a housing 40 on itsouter surface and is held to the inner mandrel by a spring nut 39. Anactuation reservoir 26 is provided in the annular space between thespring body 22 lower end and actuation mandrel upper end and theactuation sleeve 25. Prior to the bridge plug assembly 10 being deployedinto a wellbore, fluid can be provided in the plunger reservoir 20 andactuation reservoir 26. The fluid can be at the substantially the samepressure. In an example, the pressure in the reservoirs 20, 26 is lessthan pressure within a wellbore.

Referring now to FIG. 4B, the plunger module 16 has moved from itsposition in FIG. 4A and toward the plug section 30. As noted above, thiscan occur by actuating valving (not shown) that communicates fluid fromthe wellbore to the plunger reservoir 20. As further depicted in FIG.4B, the plunger sleeve 17 has moved downward due to a pressuredifferential against the shoulder 21 caused by the higher pressurewellbore fluid. This movement enlarges the plunger reservoir 20 andsignificantly reducing the volume in the actuation reservoir 26. In analternative, this can be caused by selectively actuating valving withinthe manifolds 19, 28, 34 or pressurizing the plunger reservoir 20thereby expanding its volume to allow the actuation sleeve 25 to axiallyslide as shown.

Fluid from the actuation reservoir 26 may flow into an annular reservoir43 shown defined between the actuation sleeve 25 and plug mandrel 33.This fluid can also fill the expanded plug section. Once the bridge plugassembly 10 is set and blocks flow in the tubular 8, the deploymentmodule 12 can be removed thereby exposing a side of a spring piston 53to pressure in the wellbore. Below the spring piston 53 is the spring23A, shown in a compressed configuration due to a pressure differentialbetween the upper end of the spring piston 53 and lower end of thespring 23A. The bridge plug assembly 10 can be removed by reinsertingthe deployment module 12 and actuating valving or ports to eliminate anypressure differentials across the shoulder 21. In an example, a valveactuator 45 is shown circumscribing the plug mandrel 33 and adjacentlateral ports in the plug mandrel 33. Wellbore fluid may be introducedinto the reservoir 43 by actuation of the valve actuator 45 to registerthe lateral ports to a flow path (not shown) in communication with thereservoir 43. Further communicating the higher pressure fluid to theactuation reservoir 26 eliminates the pressure differential on theshoulder 21. A valve sleeve 47 shown circumscribing the actuationmandrel 27 adjacent the valve actuator 45 can be axially manipulated toregister lateral ports in the mandrels 33, 27 for fluid communication tothe reservoirs 43, 26. Removing the pressure differential allows thespring 23 to expand and exert an axial force that is ultimatelytransmitted to the base sub 38 for returning the plug section 30 to itsoriginal configuration of FIG. 4A. A valve V^(P) is shown in the springpiston 53 that may optionally be opened to equalize fluid pressurebetween the wellbore and adjacent the spring 23.

In an alternative example embodiment, the plug section 30 includes thespring 32 shown helically wound around the plug mandrel 33 and coveredwith the flexible member 31. As discussed above, the spring 32 istorqued into the insertion or cylindrically shaped configuration (FIGS.3A and 3B) and held in place in the embodiment of FIG. 4A. Without theresistance of the fluid trapped in the actuation reservoir 26, force inthe torqued spring 32, unwinds the spring 32 allowing to radially expandas it slides the actuation sleeve 2 downward. After the flexible member31 has radially expanded to sealingly engage the tubular 8, the valvingwithin the manifolds 19, 28, 34 can be shut and the deployment module 12removed as illustrated in FIG. 4C.

The present invention described herein, therefore; is well adapted tocarry out the objects and attain the ends and advantages mentioned, aswell as others inherent therein. While a presently preferred embodimentof the invention has been given for purposes of disclosure, numerouschanges exist in the details of procedures for accomplishing the desiredresults. These and other similar modifications will readily suggestthemselves to those skilled in the art, and are intended to beencompassed within the spirit of the present invention disclosed hereinand the scope of the appended claims.

1. A bridge plug assembly for plugging a tubular within a wellborecomprising: an elongate mandrel; an actuation sleeve circumscribing themandrel; a first reservoir within the actuation sleeve; a plug sectionon the mandrel and adjacent the actuation sleeve and selectivelymoveable from a substantially cylindrical insertion configuration to aradially bulging plugging configuration; a second reservoir disposedbetween the first reservoir and the plug section; and a sealing barrierbetween the first and second reservoir and coupled to the actuationsleeve, so that when pressure in the first reservoir exceeds the secondreservoir, the barrier is urged into the second reservoir and theactuation sleeve is urged into compressive engagement with the plugsection to move the plug section to the radially bulging pluggingconfiguration.
 2. The bridge plug of claim 1, further comprising aselectively open and closed valve having an end in fluid communicationwith the wellbore and an opposite end in fluid communication with thefirst reservoir.
 3. The bridge plug of claim 1, further comprising aselectively open and closed valve having an end in fluid communicationwith the wellbore and an opposite end in fluid communication with thesecond reservoir.
 4. The bridge plug of claim 1, further comprising aflow circuit in the mandrel made up of axial and radial passages thatinterconnect and a valve actuator coupled with the mandrel thatselectively provides fluid communication between the flow circuit andthe second reservoir.
 5. The bridge plug of claim 1, further comprisinga flow circuit in the mandrel made up of axial and radial passages thatinterconnect and a valve actuator coupled with the mandrel thatselectively provides fluid communication between the first reservoir andthe second reservoir.
 6. The bridge plug of claim 1, further comprisinga deployment module attachable to an end of the actuation sleeve.
 7. Thebridge plug of claim 1, further comprising a spring coaxially disposedin the mandrel and selectively compressible, so that when fluid pressureacross the barrier is equalized, the spring axially expands andselectively moves the plug section to the substantially cylindricalinsertion configuration.
 8. The bridge plug of claim 1, furthercomprising an outer shell on the outer periphery of the plug sectioncomprising a nickel titanium alloy.
 9. A method of plugging a tubularwithin a wellbore comprising: providing in the tubular a bridge plugassembly having a mandrel, an actuation sleeve circumscribing themandrel, and adjacent the sleeve a plug element on the mandrel that isselectively configurable between a substantially cylindricalconfiguration to a bulbous configuration; and axially urging theactuation sleeve against the plug element by directing pressure from thewellbore along the axis of the bridge plug assembly so that the plugelement changes from the substantially cylindrical configuration intothe bulbous configuration to plug the tubular.
 10. The method of claim9, wherein the bridge plug assembly further comprises a reservoir and apiston axially slidable into the reservoir and that is coupled with theactuation sleeve.
 11. The method of claim 9, wherein the bridge plugassembly further comprises a resilient member axially disposed in themandrel, the method further comprising compressing the spring by forminga pressure differential along the spring.
 12. The method of claim 11,further comprising removing the pressure differential along the springso that the spring exerts a force to expand and directing the springforce across the plug element so that the plug element returns to thesubstantially cylindrical configuration from the bulbous configuration.13. The method of claim 9, wherein the plug element comprises an outershell formed from a nickel titanium alloy.
 14. The method of claim 9,wherein the plug element comprises an outer shell formed from anelastomer.
 15. The method of claim 9, wherein a flow circuit is providedin the mandrel and made up of axial and radial passages thatinterconnect and a valve actuator coupled with the mandrel thatselectively provides fluid communication between the first reservoir andthe second reservoir, the method further comprising actuating the valveactuator to provide fluid communication between the first and secondreservoirs.
 16. The method of claim 9, wherein the bridge plug assemblyfurther comprises a flow circuit in the mandrel made up of axial andradial passages that interconnect and a valve actuator coupled with themandrel that selectively provides fluid communication between the flowcircuit and the second reservoir, the method further comprisingactuating the valve actuator to provide fluid communication between theflow circuit and the second reservoir.
 17. The method of claim 9,wherein the bridge plug assembly further comprises an actuation module,the method further comprising removing the actuation module from thebridge plug assembly.
 18. The method of claim 17, the method furthercomprising reattaching the actuation module to the bridge plug assembly,actuating a valve in the bridge plug assembly to equalize pressure tothe actuation sleeve, and moving the plug element so that the plugelement changes to the substantially cylindrical configuration from thebulbous configuration, and removing the bridge plug assembly from thetubular.
 19. The method of claim 17, wherein the step of moving the plugelement so that the plug element changes to the substantiallycylindrical configuration from the bulbous configuration comprisingcompressing a spring within the mandrel with a pressure differential,then removing the pressure differential along the spring so that thespring exerts a force to expand and directing the spring force acrossthe plug element so that the plug element returns to the substantiallycylindrical configuration from the bulbous configuration.